The present invention generally relates to an implantable cardioverter/defibrillator. The present invention more particularly relates to such a cardioverter/defibrillator having arrhythmia termination shock delivery timing which avoids shock delivery during vulnerable periods of the heart.
There is an increasing problem with ventricular defibrillation and cardioversion shocks causing atrial fibrillation. This is due to the tendency towards the use of a xe2x80x9csingle-passxe2x80x9d lead, the use of a xe2x80x9chot canxe2x80x9d and the progressive decreasing of energy requirements for ventricular cardioversion and defibrillation. The single-pass lead, of the type known in the art, includes an atrial or superior vena cava shock coil for positioning in the right atrium or superior vena cava and a ventricular shock coil for positioning in the right ventricle. Hot can usage encompasses the use of the electrically conductive device enclosure as a defibrillation electrode wherein the cardioversion or defibrillation shocks are delivered from the ventricular shock coil to the atrial/superior vena cava shock coil and the electrically conductive device enclosure. Prior to the hot can approach, a subcutaneous patch electrode was used. The hot can approach causes more current flow through the atria than was caused when using the subcutaneous patch.
Extremely high energy shocks cardiovert or defibrillate the entire heart and thus preclude induction of atrial fibrillation during ventricular cardioversion or defibrillation. However, the trend is to employ more moderate energy shocks for ventricular cardioversion and defibrillation. These reduced energy shocks may not cardiovert or defibrillate the atria during ventricular cardioversion and defibrillation thus increasing the probability of inducing atrial fibrillation as a result of ventricular cardioversion or defibrillation.
The induction of atrial fibrillation by ventricular arrhythmia shock therapy causes a cascading sequence of problems. The delivery of the ventricular shock usually occurs during a period of patient unconsciousness and is not felt. However, after atrial fibrillation is induced, the patient is left with significant anxiety that there is still an arrhythmia. This can lead to inappropriate decisions on the part of the patient, as well as the implantable ventricular cardioverter/defibrillator. For example, the implanted device can mistake the atrial fibrillation for a ventricular arrhythmia and thus cause another shock to be delivered to the patient. This second shock is often extremely painful, for the patient will now be conscious. The second delivered shock, moreover, will most likely merely serve to ensure that the patient remains in atrial fibrillation.
The atrial period of vulnerability is a period of time during which atrial fibrillation is more easily induced and is analogous to the ventricular period of vulnerability. It follows shortly after the P-wave. Ventricular shocks delivered during this period are more likely to induce atrial fibrillation.
Generally, ventricular defibrillation shocks are delivered synchronized to a sensed R-wave to avoid the potential ventricular fibrillation induction in the case of a false positive ventricular fibrillation discrimination. Therefore, in a ventricular defibrillator also employing dual chamber pacing, ventricular defibrillation shock timing would be advantageous. It would also be advantageous to base shock timing on both the atrial and ventricular intrinsic and paced activity. The same reasoning applies equally as well to an atrial defibrillation shock and the induction of ventricular fibrillation.
The invention provides an implantable cardioverter/defibrillator which applies a quantity of electrical energy to a heart to terminate an arrhythmia of the heart. The cardioverter/defibrillator employs therapy delivery timing to avoid delivery of the therapy during vulnerable periods of the heart. The cardioverter/defibrillator includes an arrhythmia detector that detects a ventricular or atrial arrhythmia of the heart, a ventricular activation detector that detects ventricular activations of the heart, and an atrial activation detector that detects atrial activations of the heart. A ventricular timer, resettable by detected ventricular activations, and an atrial timer, resettable by detected atrial activations, keep time responsive to the arrhythmia detector detecting the arrhythmia. A generator applies the quantity of electrical energy to the heart responsive to the arrhythmia detector detecting the arrhythmia, the ventricular timer, and the atrial timer.
In accordance with a primary aspect of the present invention, the ventricular timer and atrial timer of the implantable cardioverter/defibrillator keep time through vulnerable intervals corresponding to vulnerable periods of the ventricles and atria respectively and the generator withholds application of the quantity of electrical energy to the heart responsive to one of the timing means being in a vulnerable interval.
In accordance with another aspect of the present invention the ventricular timer and atrial timer of the implantable cardioverter/defibrillator keep time through safe intervals corresponding to absolute refractory and rest periods of the ventricles and atria respectively and the generator applies the quantity of electrical energy to the heart responsive to both of the timers being in one of the safe intervals.
The invention further provides an implantable cardioverter/defibrillator which applies a quantity of electrical energy to a heart to terminate a ventricular arrhythmia. The cardioverter/defibrillator includes a ventricular arrhythmia detector that detects ventricular arrhythmias, an atrial activation detector that detects atrial activations, and a generator that delivers the quantity of electrical energy to the heart responsive to the ventricular arrhythmia detector detecting a ventricular arrhythmia and at a predetermined safe time after detection of an atrial activation by the atrial activation detector.
The present invention still further provides a method of applying a quantity of electrical energy to a heart to terminate an arrhythmia of the heart. The method includes the steps of detecting a ventricular or atrial arrhythmia of the heart, detecting ventricular activations of the heart, and detecting atrial activations of the heart. The method further includes the steps of keeping a first time from each detected ventricular activation after the detection of the arrhythmia of the heart, keeping a second time from each detected atrial activation after the detection of the arrhythmia of the heart, and applying the quantity of electrical energy to the heart after detecting the arrhythmia of the heart and responsive to the first kept time and the second kept time.
In accordance with a further aspect of the present invention, the first kept time and the second kept time extend through vulnerable intervals corresponding to vulnerable periods of the ventricles and atria respectively, and application of the quantity of electrical energy to the heart is withheld when one of the kept times is in a vulnerable interval.
In accordance with further aspects of the present invention, the first kept time and the second kept time extend through safe intervals corresponding to absolute refractory and rest periods of the ventricles and atria respectively and the quantity of electrical energy is applied to the heart when both of the kept times are in one of the safe intervals.
The invention still further provides a method of applying a quantity of electrical energy to a heart to terminate a ventricular arrhythmia including the steps of detecting a ventricular arrhythmia of the heart, detecting atrial activations of the heart, and delivering the quantity of electrical energy to the heart after detecting the ventricular arrhythmia and a predetermined time after detecting an atrial activation.